Two Michigan Tech researchers study exercise habits, health and whether standing or
sitting while working affects how arteries stiffen.

By now you’ve probably heard the edict from the health community: Sitting is the new
smoking. Perhaps you’ve converted to a standing desk, or maybe you have a reminder
on your phone to get up once an hour and walk around the office a few times.

But are there consequences to your arteries whether you’re sitting or standing? Two
researchers at Michigan Technological University have set out to answer this question.

Shock Through the Heart

John Durocher, assistant professor of biological sciences, and Ian Greenlund, a master’s
degree student in biological sciences, have spent the past few months conducting physical
tests on volunteers to determine whether sitting or standing has an effect on the
stiffness of arteries.

As humans age, our arteries gradually stiffen. Consider a garden hose versus a narrow
steel pipe: The walls of the hose are flexible, while the narrow steel pipe has no
give. When our heart contracts, it not only pumps blood into our arteries, it creates
a pulse wave. This is what you feel when you find a pulse at your wrist or neck. This
wave is a pressure that moves through the walls of our arteries at a flow velocity
of about four to six meters per second as the blood vessels expand and recoil.

In people with prehypertension or hypertension, the stiff arteries act as rigid and
dense conduits, and the pulse wave velocity quickens to 10 meters per second or higher.
Remember in grade school when you learned sound waves travel faster through solid
objects? The same principle applies to the pressure waves in your arteries.

With each pulse wave that is created, a reflected wave is sent back toward the heart
as our large arteries branch off into smaller arteries. Reflected waves are not always
a bad thing. It’s the timing of the reflected wave that can pose an issue. If the
rebound of that pressure wave returns to the heart during diastole—when the muscle
relaxes—it can help supply more blood through the coronary arteries to better oxygenate
the heart muscle. But if the reflected wave comes before the end of systole—when the
heart contracts—it can increase the aortic blood pressure.

“Essentially the heart has to work harder and contract more forcefully,” Greenlund
says. “If that happens over a long period of time, it can lead to heart failure or
a heart attack.”

To determine whether standing or sitting for work influences arterial stiffness, Durocher
and Greenlund studied 48 people classified into four groups—stands most of the day
for work and is physically fit, stands most of the day for work and has lower fitness
levels, sits most of the day for work and is physically fit, and sits most of the
day for work and has lower fitness levels—over the course of nine months.

"What I’m interested in is to see what people can do to live a healthier lifestyle.
There are a lot of little choices we can make. One might be standing, one might be
taking a walk at lunch time, one might be eating better, one might be getting better
sleep."John Durocher

To determine a baseline of fitness and activity, participants in the study wore accelerometers
around their wrists for two weeks to track their sleep and activity (much like a FitBit),
as well as participating in a Rockport walk test to gauge fitness levels. Greenlund
also measured distances from the suprasternal notch (that divot between your collar
bones at the base of your neck) to the radial, carotid, femoral and dorsalis pedis
arteries at the wrist, neck, groin and foot, respectively. Taking these measurements
allows the researchers to estimate a pulse wave velocity in meters per second.

Durocher and Greenlund also took resting blood pressure measurements using applanation
tonometry—a pencil-like device placed against the artery of interest. Finally, participants
were measured on a scale that uses bioelectrical impedance to calculate body fat content
by passing a current through the body. Fat is water-poor and so has higher resistance
to the current; more impendence indicates higher body fat.

Using all of these measurements, as well as a questionnaire about weekly physical
activity, the researchers are able to calculate how stiff a person’s arteries are
and examine differences between seated and standing groups along fitness classifications.

Lifestyle Choices

In this study, researchers did not find significant differences when comparing seated
and standing desk groups across fitness levels. However, with the help of Min Wang,
associate professor of mathematical sciences, the researchers employed a step-wise
linear regression analysis on multiple predictors to determine which variables were
more likely to result in increased arterial stiffness.

Carotid-femoral pulse wave velocity, which estimates stiffness within the central
region of the body and is considered the gold-standard indicator of arterial health,
was best predicted by age, followed by waist circumference. Essentially, younger participants
in the study with trimmer waists experience lower pulse wave velocities, indicating
more supple arteries. Additionally, leg pulse wave velocity values were best predicted
with fitness levels, followed by waist circumference—fitter participants in the study
with trimmer waists experience lower pulse wave velocities.

These results, and others, indicate that arteries stiffen with age. However, there
are particular lifestyle interventions like exercising more often, increased physical
activity and healthier eating that may help to reduce waist circumference and increase
fitness. While standing at work does not appear to have a direct benefit on arterial
stiffness, it is apparent that healthy lifestyle choices can reduce cardiovascular
risk.

The moral of the story is this: Instead of spending the Thanksgiving holiday parked
in front of the TV watching the Lions play the Vikings, get up and throw the pigskin
with the relatives. Go on a walk. And don’t wait for the New Year to resolve to spend
more time standing than sitting.

Michigan Technological University is a public research university, home to more than
7,000 students from 54 countries. Founded in 1885, the University offers more than
120 undergraduate and graduate degree programs in science and technology, engineering,
forestry, business and economics, health professions, humanities, mathematics, and
social sciences. Our campus in Michigan’s Upper Peninsula overlooks the Keweenaw Waterway
and is just a few miles from Lake Superior.

About the Author

Kelley Christensen

Kelley writes university research stories and articles for university publications.
She studied news-editorial journalism and American literature at the University of
Nebraska-Lincoln and holds a master's in technical communication from Montana Tech.
She is pursuing her doctorate in environmental policy at Michigan Tech.